The way that it works is that seats get filled up by those who have shown an interest in the subject and have the best grades.
Let's say for Computer Science, there are 40 seats. If applications come from 100 students, only the best 40 students will get a place.
However if for a course like sociology where there is less demand but still 40 seats, someone with not so good grades can get in. They'll give priority to the best results first and then lower their standards, otherwise it would be a waste of space.
So fill in your UoM application but try to aim for courses with less demand to increase your chances of securing a place.
Good luck :)